1. In a large cohort study, infants whose mothers received the BNT162b2 vaccine during pregnancy were not significantly more likely to be born preterm.
2. There were no significant differences in infant mortality, congenital anomalies, or infant hospitalization based on maternal vaccination status.
Evidence Rating Level: 2 (Good)
Study Rundown: Pregnant patients were excluded from early trials of COVID-19 vaccinations, including Pfizer-BioNTech’s BNT162b2 mRNA vaccine. The vaccine is now recommended and routinely administered in pregnancy in part due to early studies suggesting a high degree of safety. However, this is the first large-scale study reporting neonatal outcomes for this vaccine. Nearly 17,000 Israeli infants with prenatal vaccine exposure were compared to about 7,600 infants unexposed to vaccine. Median follow-up was about 4.5 months, with a minimum of one month. There was no association between vaccine exposure and rates of preterm birth, low birth weight, or very low birth weight. There were also no significant between-group differences in rates of all-cause infant mortality, all-cause neonatal or post-neonatal hospitalizations, or phototherapy during the study period. Infants whose mothers were vaccinated during the first trimester were not significantly more likely to have congenital malformations. Non-singleton births and stillbirths were excluded from the study, which could potentially prevent detection of some risks. The inherent limitations of observational data are difficult to avoid at this stage of COVID-19 vaccination given that pregnant women were excluded from initial preauthorization trials. However, this large cohort study provides broad and compelling evidence supporting the safety of the BNT162b2 vaccine in pregnant women with respect to infant outcomes. Providers can thus be even more confident in recommending this vaccine to pregnant patients.
Relevant Reading: mRNA COVID-19 vaccines in pregnancy: A systematic review
In-Depth [retrospective cohort]: Data were obtained from a database including 26.7% of the Israeli population. 24,288 live births between March and September 2021 were included. Within the group unexposed to the vaccine, 2,241 infants were exposed to a maternal SARS-CoV-2 infection. Stabilized inverse probability of treatment weights (IPTWs) were used to balance the groups with respect to baseline maternal demographics, including maternal age, parity, and socioeconomic status. Rates of early preterm birth were significantly higher in the unexposed group with a risk ratio of 0.45 (95% confidence interval 0.29-0.70), though there was no significant difference in overall preterm birth. Analysis of risk of congenital anomaly was performed in a subgroup including only infants whose mothers were vaccinated in the first trimester, yielding a risk ratio of 0.69 (0.44-1.04) for vaccine exposure. In a sensitivity analysis excluding mothers who had SARS-CoV-2 infection during pregnancy, the only change in relative outcomes observed was a significantly increased risk of jaundice requiring phototherapy in vaccine-exposed infants (1.46; 1.06-2.06).
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